Advanced multi-antenna technology is one of the key technologies of Long Term Evolution Advanced (LTE-A or LTE-Advanced) system, and is used for improving the system transmission speed. In order to realize the channel quality measurement and data demodulation after the advanced multi-antenna technology is introduced, the LTE-A system is defined into two types of pilot signals: DMRS and Channel State Information-Reference Signal (CSI-RS), wherein the DMRS is used for the demodulation reference signal of Physical Downlink Shared Channel (PDSCH), and the measured reference signal CSI-RS of Channel State Information (CSI) is used for the information reporting of Channel Quality Indicator (CQI), Precoding Matrix Indicator (PMI), Rank Indicator (RI) and the like. The structures of the two types of reference signals can be used for supporting new technology of LTE-A system such as Coordinated Multi-Point (CoMP) and spatial multiplexing.
In the LTE system, the pilot frequency is measured by adopting Common Reference Signal (CRS), that is, all users use public pilot frequency to perform channel estimation; the CRS needs a transmitting side extra notification message to notify the receiving side which pre-treatment process is adopted for transmitted data, and the extra notification message brings about extra overhead. Moreover, in MU-MIMO, a plurality of CRSs used by the UE are the same, which cannot realize the orthogonality of the pilot frequency. Therefore, the interference cannot be estimated.
In the LTE-A system, in order to reduce the overhead of pilot frequency, CSI-RS and DMRS are separately designed, wherein DMRS and data adopt the same pre-treatment process; meanwhile, DMRS is particularly mapped according to available rank information of the channel for scheduling user. Therefore, the overhead can be adjusted in a self-adaptive manner according to the rank information so that the overhead can be greatly reduced in the condition of relatively smaller rank.
FIG. 1 shows a diagram of DMRS bearing in normal sub-frame and specific sub-frame under normal Cyclic Prefix (CP) in the LTE_A system. As shown in FIG. 1, the design pattern of the DMRS has already been determined in the current discussion, wherein only the RE corresponding to the sand point grid shown in the diagram is used for bearing the DMRS when the rank number used in the downlink transmission is less than or equal to 2, and Orthogonal Cover Code (OCC) with a length of 2 is adopted for scrambling two adjacent Orthogonal Frequency Division Multiplexing (OFDM) symbols in time domain. Two sets of RE are used for bearing the DMRS when the rank number is greater than or equal to 3 and less than or equal to 4, and the two sets of RE are respectively corresponding to the sand point grid and the graticule line grid in the diagram, wherein the DMRS layer number of the maximum orthogonal Code Division Multiplexing (CDM) in each set of RE is 2, and the orthogonal cover code with a length of 2 is adopted for performing orthogonal scrambling on the two adjacent OFDM signals in time domain simultaneously in each set. While the OCC code with a length of 4 is adopted for performing orthogonal scrambling in time domain direction in each set of the two sets of RE for bearing the DMRS when the rank number is greater than 4, and the DMRS layer number of the maximum orthogonal CDM in each set of RE is 4. In FIG. 1, the left diagram is a diagram of the DMRS bearing in a normal sub-frame, and the middle diagram and the right diagram are diagrams of the DMRS bearing in a specific sub-frame.
According to the DMRS mapping shown in FIG. 1, a mixed multiplexing of Frequency Division Multiplexing (FDM) and CDM is introduced. Therefore, transmitting powers corresponding to different layers of the resource element for bearing the DMRS can be different when the total layer number is odd, and the transmitting power with total layer number is 2 is different from that with total layer number is even but excluding 2.